PROJECT SUMMARY Among the most devastating opportunistic diseases associated with human immunodeficiency virus (HIV) are those that affect the central nervous system (CNS). Their nonspecific presentation makes diagnosis difficult even in the best-resourced settings, and in Low and Middle Income Countries (LMICs), a definitive diagnosis can be all but impossible. In this context, CNS infections such as toxoplasmic encephalitis (TE) and CNS Chagas disease are often treated empirically, which can be fatal when physicians' best guesses are incorrect. Toxoplasma gondii seroprevalence is estimated to be highest in Latin America, but diagnosis in HIV-positive patients is difficult without expensive technologies that are unavailable in resource-poor countries. Similarly, Chagas disease, caused by Trypanosoma cruzi, is a serious opportunistic infection in people living with HIV/AIDS, and is also difficult to diagnose. Finally, tuberculosis meningitis (TBM) is difficult to diagnose and frequently fatal because of the delay in diagnosis. 33% of Peruvians and Bolivians are at risk for the development of TB, when patients are HIV positive they are at risk of TBM. Much of South America, including our study site in Bolivia, is highly endemic for both T. cruzi and T. gondii as well as other common CNS opportunistic pathogens. We propose the development and pilot testing of a novel diagnostic assays and their use in clinical diagnosis of TE and CNS Chagas disease through the following aims: Specific Aim 1: Development of parallel lateral flow assays for TE, TBM, and CNS Chagas. In addition to our already developed dot blot assays for Chagas and TB, we have preliminary data that demonstrates nanoparticles' ability to capture and detect multiple T. gondii antigens. (3-5) With further development, we will be able to transition these individual immunoassays into a simultaneous lateral flow test. Specific Aim 2. To determine the sensitivity and specificity of the nanoparticle diagnostic assays for TE, TBM and CNS Chagas disease in a well-characterized cohort of HIV-infected patients with acute neurological syndromes. We expect that the proportion of neurological syndromes due to toxoplasmosis, TBM, and cryptococcal meningitis will be similar to those in other South American HIV populations. We anticipate, however, that CNS Chagas disease will also cause a substantial proportion of neurological disease in the Bolivian population, which may have been underdiagnosed. This project will help define the clinical spectrum of HIV-associated neurological disease in Latin America and use innovative diagnostic techniques to distinguish between CNS Chagas disease, TBM, TE, and other CNS infections. Where multiple pathogens are endemic and are rapidly fatal, more rapid, sensitive, and specific tests could accelerate the initiation of specific and potentially life-saving therapy.